SUMMARY A wide variety of toxic chemicals could be used in a terrorist attack, with the Centers for Disease Control and the Department of Homeland Security listing over 80 potential chemical threat agents. Unfortunately, specific antidotes that can be administered quickly in the field are not available for many of these chemicals. We have found that three of these agents-hydrazine, sodium azide, and hydrogen sulfide, all of which are considered high priority chemical threats and for which no good antidote exists--bind with high affinity to cobinamide, the penultimate precursor in cobalamin (vitamin B12) biosynthesis. We are currently developing cobinamide as a cyanide antidote, and have found it to be extremely effective at neutralizing cyanide in cultured mammalian cells, Drosophila melanogaster, and mice and rabbits. Cobinamide is non-toxic to mice and rats up to doses of 500 mg/kg, and, in June, 2009, we had a pre- Investigators New Drug (IND) meeting with the Food and Drug Administration concerning the use of cobinamide as a cyanide antidote. We anticipate starting Phase I Clinical Trials and pivotal animal studies of cobinamide by Winter, 2012. Because of the extreme toxicity of cyanide, it cannot be given to humans, and, thus, cobinamide will need to be approved through the Animal Rule Pathway, in which randomized placebo-controlled studies in two animal species replace Phase II and III Clinical Trials. Thus, cobinamide could become available on the market relatively soon. It would be extremely useful if it could be used as a countermeasure against other chemical threat agents in addition to cyanide. We now propose to determine if cobinamide can be used as an antidote against hydrazine, sodium azide, and hydrogen sulfide by following the same paradigm as during the early development phase of cobinamide as a cyanide antidote. Specifically, we plan to determine cobinamide's efficacy as an antidote against these three chemical agents in cultured cells and D. melanogaster. If cobinamide is effective in either or both these model systems, we will then study its efficacy in a lethal mouse model. The proposed work could lead to a treatment for one or more chemical threat agent for which no effective therapy currently exists, allowing one antidote to be used against more than one chemical threat. Moreover, resources will be saved because most of the pre-clinical toxicology and pharmacokinetic studies, and the Phase I Clinical Trials, will have already been done.